Light emitting diodes (LEDs) are being used more frequently as a light source for signal lamps such as traffic lights. FIG. 1 is a cross sectional diagram illustrating a conventional signal lamp 100 currently in use within the industry. Signal lamp 100 includes a housing 110 having an opening 120 closed by a spreading window 130. The signal lamp 100 further includes high power LEDs 140, mounted on substrate 150, and a lens 160 located substantially parallel to the substrate 150. Lens 160 is located at a distance from the LEDs that achieves a desired homogeneous light output.
One current industry practice involves implementing the lens 160 as a Fresnel lens and locating the LEDs 140 in a region corresponding to the inner 25% of the area of lens 160. Another industry practice involves locating the LEDs 140 in a region corresponding to the inner 10% of the area of the lens 160. When an LED fails, this configuration provides a smaller reduction in the homogeneity of the brightness distribution on the surface of the spreading window 130 than in signal lamps that are not provided with a Fresnel lens and in which the LEDs are distributed on the entire area of lens.
The signal lamp 100 of FIG. 1 is susceptible to problems associated locating the high-power LEDs 140 in a region corresponding to the inner 25% of the area of the lens 160. High temperatures caused by thermal buildup can result in premature LED failure. Location of the high power LEDs 140 in the region corresponding to the inner 25% of the area of the lens 160 also requires that the lens 160 be located a greater distance from the high-power LEDs 140 to achieve a desired homogeneous light output. The greater distance results in a corresponding increase in the depth of the housing 110.
It would be desirable, therefore, to provide a signal lamp and a method of making a signal lamp that would overcome these and other disadvantages.